Breathing apparatuses are widely used in settings in which people risk exposure to dangerous airborne hazards. Various types of breathing devices are employed to provide protection against various dangers. For example, some breathing filters provide protection against particle contaminants. Some breathing apparatuses provide filtration of chemical hazards. Other breathing devices provide defense against nuclear unstable gaseous elements.
In some industrial situations, workers may breathe breathable air provided to them from safe sources. Some workers wear air tight suits which may be supplied clean air via a hose or air line. Some workers may carry clean air in a cylinder or compressed-air tank. Scuba divers may carry one or more air tank on their back, each of which may provide breathable air to the divers while underwater.